I voted single-ended. One of the major engineers at Benchmark is on record as saying the benefits as oft' advertised simply don't exist(AMB forum); even as a layperson looking at it it's not clear what you get for doubled output impedance and other tradeoffs.

It is worth noting that AMB contested some of these claims, but I side *very* strongly with the Benchmark engineer on this one.

Initial message expressing opinion on debate:

Hello!

My name is Elias Gwinn, I'm an engineer at Benchmark Media Systems.

We've been getting a lot of questions lately about balanced headphones. We are interested in the debate, but I can't say we agree with any technical explanations about the benefits of the set up.

So far, there are 4 major points mentioned so far (that I have heard, at least):

1. Unshared common conductor reduces crosstalk

2. Two amps (per channel) increases slew-rate

3. Two amps provide better damping

4. Balanced cabling provides better common-mode rejection

If I may, I'd like to add my thoughts on these points:

1. Most headphones (at least those of decent quality) do not share a common conductor through the length of the cable (as opposed to what was said in 6 Moons). Most headphones have a separate wire from each negative terminal that remain isolated through the length of the cable. In other words, most headphone cables are effectively balanced inherently. If they were sharing a common through the length of the cable, the impedance of the cable may cause some of the signal to show up on opposing channels. However, they are not connected until the plug, and therefore have a minimal impedance to ground.

2. Any headphone amp that is struggling with slew-rate is a poorly designed headphone amplifier. The HPA2 headphone amplifier on the DAC1 has a bandwidth of 55 kHz, and it doesn't even approach any slew-rate limitations even at those high frequencies.

3. Two amps provide WORSE damping. This is why power amplifiers run better in normal mode vs. bridged mode. A balanced (dual-active) headphone amplifier is exactly analogous to a bridged amplifier driving one speaker. The only advantage is increased power, but it comes at an expense of increased distortion, decreased damping, and altered frequency response. This is common knowledge for bridged amplifiers.

4. Headphones don't need any help with common-mode rejection because they inherently will not respond to common mode signal. If, for example, you apply a signal to both terminals of a speaker, it will not move at all. A speaker only responds to differential voltages.

5. There is another cost incurred by dual-active headphone amps that is not addressed. Headphone amps should have as low of a source impedance as possible. If you are using two amps to drive a channel, you are doubling the source impedance. This will cause the headphones to suffer in frequency response, distortion, and ringing.

Please continue the great discussions. It is important to resolve these debates so that product manufactures can respond to provide the best audio solutions possible.

Thanks!
Elias Gwinn

Second response to similar query:

ALL headphones have non-linear mechanical impedances (that is, the mass and shape of a speaker will resonate more at certain frequencies and much less at other frequencies). This means the physical build of the headphones (as well as other physical impedances, like your head and ears!) will try to override the electrical system (amplifier and speaker coil).

To create low-distortion headphone response, one must consider 'damping factor'. A high damping factor will control the response of the speaker, thus preventing the physical impedances from dictating frequency response. Damping factor is the ratio of speaker (load) impedance to amplifier (source) impedance. In other words, the best damping factor will result from a low source impedance. Again, the source impedance from the HPA2 is less then 0.01 ohms...as low as gets!!

Balanced headphone amps will double the source impedance of an unbalanced headphone amp. No matter how low the impedance of a balanced headphone amp, it could be half that much if it was unbalanced. This is one reason balanced headphone amps are not a good idea. (It should also be noted that the balanced output of the DAC1 / USB / PRE is 60 ohms or greater, depending on the attenuator settings).

Not only will the source impedance double with balanced headphone amplifiers, but the total distortion and noise of the amplifier will double as well!! Every output device (opamp, transistor, tube) creates some distortion and some noise. If there are two opamps or transistors or tubes driving each headphone speaker, twice as much distortion and noise will be added!!

The result of balanced headphones is less damping factor, more distortion, and more noise. Also, balanced headphones configurations offer no real benefits, to boot.

Feel free to use the XLR outputs of the DAC1 / USB / PRE for balanced headphone outputs (as mentioned above, the DAC1 USB and DAC1 PRE will do better then the DAC1 at this task, because of the 4562's). It won't damage anything to operate in this configuration. But, for the reasons above, I don't recommend it.

Right, so here is the princip. What do you prefer and why? But on the following terms:

-Ignore power output (Imagine you hook a can that is only 35 ohm, or but amps just have equal power output)

-Ignore price and size

-Only sound matters, what difference does it really make?

So, is it just a power thing or would there really be a significant sound difference between the same amp section in balanced vs. unbalanced mode?

May I add one more term, which is who ever going to vote has to use a balance system for at least six months. It will not be fair to vote if one does not have sufficient experience with what a balance sound is like. Agree?

But the the question would be: Wouldn't a balanced amplifier via "push-pull" factor in turn offer superior control of the diaphragm, like a electrostatic setup does and thus provide a more accurate reproduction of sound?

And isn't the distortion level on any properly built and commercially available balanced so low pr. channel that even added up it is not near anything audible?

May I add one more term, which is who ever going to vote has to use a balance system for at least six months. It will not be fair to vote if one does not have sufficient experience with what a balance sound is like. Agree?

With that, 1 vote for balance with three years of balance use.

What have you gained in terms of sound from balanced vs. SE? And which headphones have you mainly used? High/low impedance etc. ?

going balanced eliminates cross-talk and usually means better shielding as well. i only have experience with balanced professional gear mostly. that's why headphones back then also used balanced 4-core TRS jacks or DIN/XLR connectors due to eliminate cross-talk. like how speaker amps have a separate ground/negative to eliminate cross-talk but cross-talk still happens due to the crossover limitations. headphones have the advantages due to them having no cross-over limitations so going balanced is more effective. elimination of cross-talk means more accurate 3d soundstage and imaging and faster how the headphone and amp communicates from transferring electrical energy into acoustic energy.

just impedance usually doubles going balanced since no longer the drivers are sharing a common ground cable between each other meaning sharing resistance as well and impedance has a higher fluctuation during certain frequency ranges due to impedance vs. frequency. depending on the person it might differ but their is lot of arguments like many other things that there is not much difference going from shared ground to balanced( separate negative/ground,positive).

But the the question would be: Wouldn't a balanced amplifier via "push-pull" factor in turn offer superior control of the diaphragm, like a electrostatic setup does and thus provide a more accurate reproduction of sound?

And isn't the distortion level on any properly built and commercially available balanced so low pr. channel that even added up it is not near anything audible?

push-pull is always better especially for high voltages increases and decreases. that's why you find speaker amps with push-pull design and not op-amps. op-amps can be great but their real limitation is when it comes to fluctuations of voltages and current especially when the source has massive current and voltages changes.

like to add also push-pull designs using a big power transformer is also better when it comes to impedance matching cause the transformer will lower and higher it's voltages to meet the respective impedance at the certain frequency range.Edited by RexAeterna - 10/18/11 at 10:49am

push-pull is always better especially for high voltages increases and decreases. that's why you find speaker amps with push-pull design and not op-amps. op-amps can be great but their real limitation is when it comes to fluctuations of voltages and current especially when the source has massive current and voltages changes.
like to add also push-pull designs using a big power transformer is also better when it comes to impedance matching cause the transformer will lower and higher it's voltages to meet the respective impedance at the certain frequency range.

Unless I have got totally the wrong end of the stick, this is an argument for the increased slew rate of balanced drive. I wasn't aware, however, that slew rate was a problem in the overwhelming majority of headphone amplifiers. The slew rate requirements for delivering music perfectly as far as slew rate is concerned into most headphones really are not particularly onerous and certainly not beyond the means of opamps.

push-pull is always better especially for high voltages increases and decreases. that's why you find speaker amps with push-pull design and not op-amps. op-amps can be great but their real limitation is when it comes to fluctuations of voltages and current especially when the source has massive current and voltages changes.like to add also push-pull designs using a big power transformer is also better when it comes to impedance matching cause the transformer will lower and higher it's voltages to meet the respective impedance at the certain frequency range.

hmm, not sure where you are getting this information. a transformer does not lower and raise its voltage to react to the load impedance, in fact the transformer hardly does anything at all to even power the amplifier most of the time. the stored energy in the reservoir caps supply power/transient response wrt the load and the transformer is only connected to the amp through the diode bridge for about 10% of the time. so the diode bridge and transformer are literally doing nothing most of the time. opamps can slew with the best of them, but current in most cases, for speakers anyway, is limited and many by themselves don't really have too fun a time driving low impedance headphones directly either

me, I prefer balanced for the bass response and speed, even for loads that you wouldn't think would need it, but single ended amps can sound fantastic as well in their own way, tbh although the dac1 is a good design, its hardly the last word and i'm getting a little bored of all this regurgitated O2, dac1, nwavguy diatribe.

not sure how AMB let himself go on record as saying balanced lowers output Z though

Slew rate/power is one of the things that is redundant in this discussion, only sound matters, as in accuracy, soundstaging and so on... :)

But how does a balanced amp improve (or not improve) these things? Crosstalk could help with soundstaging, but good crosstalk is not inherent to balanced amps. Many headphone amps have under 90dB crosstalk single-ended. So ultimately here wouldn't the measurement matter, not the design? A single-ended amp with better crosstalk than a balanced amp would be better for crosstalk, no discussion needed. The design helps, but isn't the most important thing.

I suppose my point is, balanced design has advantages and disadvantages, all of which a properly or improperly designed single-ended amp can meet. The issue isn't the design, but the performance. Discussing balanced vs. single-ended is a moot point without numbers.